The invention relates to a receptacle for poultry and the like including a tray or other container and a film wrapping which is positioned over the container and its contents and sealed beneath the container.
Pre-packaged poultry, poultry parts and other food products have been provided in a receptacle including a tray and a flexible thermoplastic film wrapping. The tray may be made from materials such as cardboard or styrofoam while the wrapping may be a PVC stretch film, polyethylene film, coextruded polyethylene/polypropylene film or other suitable material. PVC film has emerged as the predominant overwrap used in the industry because of its machinability on automatic equipment, the ease in which it can be formed and folded for heat sealing beneath the tray, and its memory and clarity.
Automatic packaging machinery typically employ stretch, stretch and shrink, or shrink techniques combined with heat and pressure to seal the lap areas of plastic films wrapped tightly about the tray and its contents. Such equipment is generally referred to as stretch and/or shrink wrapping machinery.
Some plastic films will, under heat, pressure and sufficient dwell time, melt together and conform to the package profile, but generally do not actually form a true surface to surface seal. Rough handling in packing and/or transportation may cause "capillary" leakage in those areas not conformed perfectly to the package.
The sealing characteristics of PVC overwrap films have never been completely satisfactory, and the problems of leaking packages having poor seals have become exacerbated during recent years with the advent of volume markets and the increase in shipping distances. The problem has lately become so evident that some supermarket chains have been supplying paper towels and/or plastic bags at the pre-packaged poultry display cases.
Coextruded films with sufficient memory for this type of packaging, such as are available to the food packaging industry, seal well under optimal conditions, but such conditions are not always possible, particularly where packaging fresh food products is concerned. Inconsistencies in the film itself may also result in leakage due to unsatisfactory sealing.
The product to be packaged may also create problems peculiar thereto in allowing a good seal to be created. For example, poultry products have irregular configurations, and the sizes thereof can vary greatly. This makes it very difficult to determine the correct amount of film required for proper wrapping and sealing. Automatic packaging systems do not ordinarily lend themselves to such adjustments.
The use of an excessive amount of film creates an insulating effect which leads to poor package conformation and sealing. To compensate for the poorer seal, the heat sealing belt temperature may be raised, but often with a "burn through" problem resulting therefrom. Too little film results in an insufficient contact area for proper sealing.
Other variables, such as variations in the size and volume per package, the temperature of the product to be packaged, and the packaging rate affect the temperature of the heat sealing belt, the pressure applied to the lap seal of the film wrapping, and the dwell time upon the heat sealing surface. The seals provided on each package accordingly may not be consistent, resulting in leakage.
A wrapping/sealing system known to the art includes a feeding belt, a wrapping machine, and a heat seal belt. A pressure unit may also be provided. Trays including poultry parts are hand fed to the feeding belt which conveys them to the wrapping machine. The wrapped, unsealed trays are ejected onto a moving heat seal belt which attempts to provide a heat seal in the areas of the flaps and lap area of the wrapping beneath the tray. Simultaneously, the trays may or may not be under pressure to improve the seal. A cooling unit may be associated with the pressure unit to help set the seal. The sealed package is then ready for packing in shipping containers and transported to the market.
One wrapping apparatus heat seals the sides of the wrapping film by drawing the lap areas together under the tray into a heated sealing wheel that provides the heat, dwell time and pressure required to form a substantially leak-proof, center sealed seam, but a sealing belt is still required to seal the front and rear flaps that fold beneath the tray.
A number of attempts have been made to improve the seal areas of film-wrapped packages. Many of these attempts have focussed on improving the sealing properties of the film itself. The films available to the food-packaging industry do not, however, provide consistently satisfactory sealing using conventional heat sealing techniques.
Other approaches for enhancing the sealing capability of plastic films has been to print adhesive directly on to the tray or to the film itself in the areas where the flaps and lap areas are to be formed. These approaches have been unsuccessful. In fact, such additions of adhesive may even interfere with the formation of a more permanent seal of the film layers by providing unwanted insulation, thereby preventing the even conduction of heat among the layers from the heat belt.
Heat sealing apparatus have been redesigned to improve their ability to seal thermoplastic films. Investments in such apparatus require significant capital, however, and still do not entirely solve problems related to leakage. Some of the more modern apparatus are energy intensive, which leads to higher operating costs as well.
Because of the inability of the industry to develop a satisfactory seal in a package including a tray and a film overwrap, several absorbent, padded trays have been proposed for absorbing fluids before they can leak through the sealed areas of the overwrap film. Chambered trays have also been proposed for trapping such fluid.
There has accordingly been a long felt need for a film-wrapped package which includes substantially leak-proof seals in the flaps and/or lap areas formed by the film, particularly a package which can be assembled using existing wrapping equipment without making substantial capital investments thereto or greatly increasing operating costs.